The present invention generally relates to actuating a moveable trim tab surface on an airfoil. More specifically, the present invention relates to actuating a moveable surface on a rotor blade using generated air pressure differentials that can be used to mimic the aerodynamic effects of a conventional trim tab surface.
Despite being fabricated to tight tolerances, helicopter rotor blades inevitably have slight manufacturing variations that cause lift and dynamic response to vary among blades. Moreover, these variations may change with time as the blade naturally wears during normal operation. In order to aerodynamically balance the blades, conventional trim tabs on the blade trailing edges are incrementally adjusted manually, introducing a large portion of rotorcraft maintenance time. It would be very advantageous if an active trim tab system was implemented that could automatically adjust trim tab angles during flight, which would greatly reduce overall helicopter vibration and maintenance time.
Various research efforts have been performed to develop an active trim tab system. There is an active trim tab actuator that uses shape memory alloy (SMA) material as the actuating mechanism. This approach, however, carries several risks with regard to operating in the rotor environment due to high force output requirements, high power efficiency requirements during actuation, and large temperature fluctuations. Also, special modifications are needed to achieve tab deflections held for long periods of time with little or no power consumption. Another approach utilizes a more traditional electromechanical actuator and a series of linkages to achieve tab motion. Despite reporting some promising results, the long term of effects of operating the actuator and linkages in very high centrifugal force remains untested and is likely to add significant design challenges.
Typically, other solutions for providing an actuator for trim tab actuation are too heavy to be practical, require excessive power, negatively increase rotor figure of merit by introducing suboptimal aerodynamic surfaces, cannot operate within the required temperature range, and require significant structural modifications to the rotor blade. In addition, the largest shortcoming of other designs is the inability to withstand the large centripetal accelerations found on rotor blades, particularly helicopter rotor blades. What is needed is a system that would provide a device that is a lightweight, actuated trim tab surface on rotor blades that contains no active outboard actuating elements, but instead contains internal actuating components that can locally actuate trim tab surfaces. It would further be advantageous to provide a retrofittable actuator system that can be mounted outboard on the rotor blade to actuate the trim tab surface.
It is an object of the present invention to provide actuation of a trim tab on a rotor blade using air pressure.